A rotary dryer/kiln is a type of industrial dryer that is used to reduce the moisture content in various materials. They are often used in the processing of cement, iron ore, limestone, plus many materials. Typical rotary dryers/kilns include a cylindrical shell that is inclined slightly in the horizontal and supported by a set of ride rings or tire rings that rest upon rollers. The contents of the dryer are heated, while the dryer is slowly rotated about its axis by rotational motion applied to the system through one of many different methods.
In one configuration, a force is applied to a tire ring through power applied to the rollers. The tires should be linked to the dryer in the radial direction and in the circumferential direction.
A typical dryer tire ring is made of a cast or forged medium carbon steel, which is machined to a smooth cylindrical surface and then hardened. It is loosely attached to the dryer/kiln shell by some variety of radial suspension methods. Several such methods exist, as some creativity is required to design for the required weight and varying load, while also allowing for thermal expansion. If a driving force needs to be conducted through the tire ring, the dryer and tire ring must be linked circumferentially, and in such a way that doesn't compromise the intent of the radial suspension. Additionally, it would be ideal for the circumferential connection method to allow free counter-rotation. Occasional, but sudden, “loaded stops” can potentially add unneeded stress to the system, if the tire ring and dryer are hard linked and slippage is not permitted to occur.
Welding to the tire ring is not ideal, as the steels used are typically not easily weldable and can be susceptible to residual stress cracking. To properly weld and treat, this material requires furnace heat treatments after welding, which can get rather costly, considering the size of the material, or may not even be feasible depending on the design and assembly order of the dryer.
Another design alternative involves the addition of a separate gear-type ring attached at a cooler part of the dryer tube. The gear is then connected though a gear train to an electric motor. This drive type adds significantly more complexity to the system, increasing cost (parts, labor, and maintenance) and the possibility for complications or failure.